Using temporary write locations for increased power efficiency

ABSTRACT

A method for a dispersed storage network (DSN) receives a data request and issues a read threshold number of read slice requests to storage units of a storage set, by receiving read slice responses from at least some of the storage units within a response timeframe and, when the received read slice responses include less than a decode threshold number of encoded data slices of a set of encoded data slices, generating at least one forced read slice request for an encoded data slice other than the received encoded data slices. The method continues by sending the at least one forced read slice requests to at least one other storage unit of the storage set and, when receiving the decode threshold number of encoded data slices, dispersed storage error decoding the received decode threshold number of encoded data slices to reproduce a data segment of the data reduce recovered data.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility Patent Application also claims prioritypursuant to 35 U.S.C. §120 as a continuation-in-part of U.S. UtilityApplication Ser. No. 15/056,517, entitled “SELECTING STORAGE UNITS IN ADISPERSED STORAGE NETWORK,” filed Feb. 29, 2016, which is acontinuation-in-part of U.S. Utility Application Ser. No. 12/903,212,entitled “DIGITAL CONTENT RETRIEVAL UTILIZING DISPERSED STORAGE,” filedOct. 13, 2010, now U.S. Pat. No. 9,462,316, which claims prioritypursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No.61/290,632, entitled “DIGITAL CONTENT DISTRIBUTED STORAGE,” filed Dec.29, 2009, all of which are hereby incorporated herein by reference intheir entirety and made part of the present U.S. Utility PatentApplication for all purposes.

U.S. Utility Application Ser. No. 15/056,517 also claims prioritypursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No.62/154,867, entitled “AUTHORIZING A SLICE ACCESS REQUEST IN A DISPERSEDSTORAGE NETWORK,” filed Apr. 30, 2015, which is hereby incorporatedherein by reference in its entirety and made part of the present U.S.Utility Patent Application for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field Of The Invention

This invention relates generally to computer networks and moreparticularly to dispersing error encoded data.

2. Description Of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network (DSN) in accordance with the present invention; and

FIG. 9A is a flowchart illustrating an example of recovering data storedin a dispersed storage network (DSN) in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 & 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data as subsequently described with reference to oneor more of FIGS. 3-8. In this example embodiment, computing device 16functions as a dispersed storage processing agent for computing device14. In this role, computing device 16 dispersed storage error encodesand decodes data on behalf of computing device 14. With the use ofdispersed storage error encoding and decoding, the DSN 10 is tolerant ofa significant number of storage unit failures (the number of failures isbased on parameters of the dispersed storage error encoding function)without loss of data and without the need for a redundant or backupcopies of the data. Further, the DSN 10 stores data for an indefiniteperiod of time without data loss and in a secure manner (e.g., thesystem is very resistant to unauthorized attempts at accessing thedata).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSTN memory 22for a user device, a group of devices, or for public access andestablishes per vault dispersed storage (DS) error encoding parametersfor a vault. The managing unit 18 facilitates storage of DS errorencoding parameters for each vault by updating registry information ofthe DSN 10, where the registry information may be stored in the DSNmemory 22, a computing device 12-16, the managing unit 18, and/or theintegrity processing unit 20.

The DSN managing unit 18 creates and stores user profile information(e.g., an access control list (ACL)) in local memory and/or withinmemory of the DSN memory 22. The user profile information includesauthentication information, permissions, and/or the security parameters.The security parameters may include encryption/decryption scheme, one ormore encryption keys, key generation scheme, and/or dataencoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particularuser, a user group, a vault access, public vault access, etc. Forinstance, the DSTN managing unit 18 tracks the number of times a useraccesses a non-public vault and/or public vaults, which can be used togenerate per-access billing information. In another instance, the DSTNmanaging unit 18 tracks the amount of data stored and/or retrieved by auser device and/or a user group, which can be used to generateper-data-amount billing information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSTN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R)of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 60 is shown inFIG. 6. As shown, the slice name (SN) 60 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

In a DSN memory, only a “Read Threshold” number of slices are actuallyrequired to service read operations. For this reason, DS units within aDSN memory may take the strategy of placing some of their memory devicesinto a power-save-mode (PSM), during which access to the data on thatmemory device is temporarily lost or degraded (e.g., powered down memorydevice, or spun down rotating disk, or decreased speed of rotation). Yetfull operation of the DSN memory requires also that a “Write Threshold”number of ds units are available to receive writes at any particulartime. To handle this, DS units which service writes destined to memorydevices that are in a PSM may instead direct those writes to temporarylocations (including other memory devices, SSDs, RAM, etc.). When theselocations become full or near full, or when the memory device for whichthe slices are destined comes out of PSM, then the DS unit may flushthese temporary locations by moving the slices to the memory device forwhich it is destined.

An additional improvement to support this scheme would be for DSprocessing units to be able to issue a “forced read” request, which maybe issued when due to availability outages and “PSM unavailability errorresponses” being returned from DS units with memory devices in PSMresults in the inability for the ds processing unit to achieve a readthreshold. This forced read request will be sent to a minimal number ofDS units needed to service the read request, and will have the effect ofbringing the memory device responsible for that slice out of PSM so theDS unit can service the read request.

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network (DSN) that includes the distributed storage and task(DST) client module 34 of FIG. 1, the network 24 of FIG. 1, and astorage set. The DST client module 34 includes inbound DST processingmodule 903. The storage set includes a set of DST execution units 902,where some of the DST execution units may, from time to time, be in apower savings mode where at least a portion of the DST execution unit ispowered down to save energy. Each DST execution unit (e.g., 1-8) may beimplemented utilizing the DST execution unit 36 of FIG. 1. Hereafter,each DST execution unit may be interchangeably referred to as a storageunit and the storage set may be interchangeably referred to as a storageunit set.

The storage set may include a number of DST execution units inaccordance with dispersal parameters of a dispersed storage error codingfunction, where the dispersal parameters includes a width n, a readthreshold number, and a decode threshold number k. The decode thresholdnumber is a minimum number of encoded data slices of a set of n encodeddata slices that is required to recover a data segment, where the datasegment is dispersed storage error encoded utilizing the dispersedstorage error coding function in accordance with the dispersalparameters to produce the set of n encoded data slices. For example, anumber of DST execution units of the DST execution unit set is n=8 whenthe width dispersal parameter is 8 and the decode threshold dispersalparameter is k=5 (e.g., requiring at least 5 encoded data slices torecover the data segment). The read threshold number includes a numberof desired encoded data slices of the set of encoded data slices forrecovery to provide the decode threshold number of encoded data slices.The DSN functions to recover data stored in the storage unit set, wheredata is dispersed storage error encoded to produce at least one set ofencoded data slices that is stored in the set of DST execution units(e.g., a data segment is encoded to produce a set of encoded data slices1-8 that are stored in the DST execution units 1-8).

In an example of operation of the recovering of the stored data, theinbound DST processing 903 receives a data request 900 to recover thedata segment. Having received the data request, the inbound DSTprocessing 903 issues a read threshold number of read slice requests tostorage units of the storage set. The issuing includes generating theread slice requests, selecting the storage units based on one or more:of a predetermination, storage unit performance levels, storage unitavailability levels, or a random selection; and sending, via the network24, the read slice requests to the selected storage units. For example,the inbound DST processing 82 selects DST execution units 1-6 and sends,via the network 24, read slice requests 1-6 to the DST execution units1-6.

Having sent the read threshold number of read slice requests, theinbound DST processing 903 receives read slice responses from at leastsome of the storage units within a response timeframe. For example, theinbound DST processing 903 receives read slice responses that includesencoded data slices 1, 2, 4, and 5 (e.g., no response from DST executionunit 3), and receives another read slice response that includes an errorresponse 6 from the DST execution unit 6.

When the received read slice responses includes less than the decodethreshold number of encoded data slices of the set of encoded dataslices, the inbound DST processing 903 generates at least one forcedread slice request for at least one other encoded data slice. Thegenerating includes determining a number of forced read slice requestbased on a number of received encoded data slices and the decodethreshold number. For example, the inbound DST processing 903 determinesto generate one forced read slice request when receiving four encodeddata slices and the decode threshold number is five.

Having generated the at least one forced read slice request, the inboundDST processing 903 sends, via the network 24, the at least one forcedread slice request to at least one storage unit of the set of storageunits. The sending includes selecting a storage unit and transmitting acorresponding forced read request to the selected storage unit. Forexample, the inbound DST processing 903 selects a storage unitcorresponding to a received error response indicating unavailability ofa corresponding encoded data slice without powering up a portion of thestorage unit. For instance, the inbound DST processing 903 selects DSTexecution unit 6 when the error response 6 indicates that the encodeddata slice 6 is unavailable without powering up a portion of the DSTexecution unit 6 and transmits, via the network 24, the forced readslice request 6 to the DST execution unit 6. As another example of theselecting of the storage unit, the inbound DST processing 903 selects aremaining storage unit of the set of storage units (e.g., selects DSTexecution unit 7).

The inbound DST processing 903 receives a further read slice response inresponse to the at least one forced read slice request from the storageset. For example, the DST execution unit 6 transitions from a powersavings mode to at least a partially active power mode to retrieve theencoded data slice 6 from a corresponding memory device, and sends, viathe network 24, the encoded data slice 6 to the inbound DST processing903. When receiving the decode threshold number of encoded data slices,the inbound DST processing 903 dispersed storage error decodes thereceived decode threshold number of encoded data slices to reproduce adata segment of the data to produce recovered data.

FIG. 9A is a flowchart illustrating an example of recovering data storedin a dispersed storage network (DSN). In particular, a method ispresented for use in conjunction with one or more functions and featuresdescribed in conjunction with FIGS. 1-2, 3-8, and also FIG. 9.

The method begins or continues at step 904 where a processing module(e.g., of a distributed storage and task (DST) client module) receives adata request. The method continues at step 906 where the processingmodule issues a read threshold number of read slice requests to storageunits of a set of storage units. For example, the processing modulegenerates the read slice requests, selects the storage units (e.g.,based on one or more of a predetermination, a performance level, arandom selection, a power savings mode, or an availability level), andsends the read slice requests to the selected storage units.

The method continues at step 908 where the processing module receivesread slice responses from at least some of the storage units within aresponse timeframe. When the received read slice responses includes lessthan a decode threshold number of encoded data slices of a set ofencoded data slices, the method continues at step 910 where theprocessing module generates at least one forced read slice request foran encoded data slice other than the received encoded data slices. Thegenerating includes determining a number of forced read slice request togenerate based on a difference between the decode threshold number and anumber of received encoded data slices.

The method continues at step 912 where the processing module sends theat least one forced read slice request to at least one storage unit. Forexample, the processing module sends the at least one forced read slicerequest to a storage unit that corresponds to an error responseindicating unavailability of an associated encoded data slice unlesspowered up. As another example, the processing module sends the at leastone forced read slice request to another storage unit outside of theselected storage units of the read threshold number of read slicerequests.

When receiving the decode threshold number of encoded data slices, themethod continues at step 914 where the processing module decodes thereceived decode threshold number of encoded data slices to reproduce adata segment of recovered data.

The method described above in conjunction with the processing module canalternatively be performed by other modules of the dispersed storagenetwork or by other computing devices. In addition, at least one memorysection (e.g., a non-transitory computer readable storage medium) thatstores operational instructions can, when executed by one or moreprocessing modules of one or more computing devices of the dispersedstorage network (DSN), cause the one or more computing devices toperform any or all of the method steps described above.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method for execution by one or more processingmodules of one or more computing devices of a dispersed storage network(DSN), the method comprises: receiving a data request; issuing a readthreshold number of read slice requests to storage units of a storageset; receiving read slice responses from at least some of the storageunits within a response timeframe; when the received read sliceresponses include less than a decode threshold number of encoded dataslices of a set of encoded data slices, generating at least one forcedread slice request for an encoded data slice other than the receivedencoded data slices; sending the at least one forced read slice requeststo at least one other storage unit of the storage set; and whenreceiving the decode threshold number of encoded data slices, dispersedstorage error decoding the received decode threshold number of encodeddata slices to reproduce a data segment of the recovered data.
 2. Themethod of claim 1, wherein the issuing includes: generating the readslice requests, selecting the storage units and sending the read slicerequests to the selected storage units.
 3. The method of claim 2,wherein the selecting the storage units is based on one or more of: apredetermination, a storage unit performance level, a storage unitavailability level, or a random selection.
 4. The method of claim 2,wherein the sending includes sending to a storage unit outside of theselected storage units.
 5. The method of claim 1, wherein the generatingis based on determining a number of forced read slice requests based ona number of received encoded data slices.
 6. The method of claim 5,wherein the generating further includes determining a number of forcedread slice request to generate based on a difference between the decodethreshold number and a number of received encoded data slices.
 7. Themethod of claim 1, wherein the sending includes sending to a storageunit that corresponds to an error response indicating no availabilityunless powered up.
 8. The method of claim 1, wherein the sendingincludes sending to temporary storage locations.
 9. The method of claim8, wherein the temporary storage locations include any of: SSDs, RAM, orother memory devices.
 10. The method of claim 9, wherein, when thetemporary storage locations become full or near full, or when the memorydevice for which the encoded data slices are destined comes out ofpower-save-mode (PSM), then the storage unit flushes these temporarylocations by moving the encoded data slices to the storage unit forwhich it was originally destined.
 11. A computing device of a group ofcomputing devices of a dispersed storage network (DSN), the computingdevice comprises: an interface; a local memory; and a processing moduleoperably coupled to the interface and the local memory, wherein theprocessing module functions to: receive a data request; issue a readthreshold number of read slice requests to storage units of a storageset; receive read slice responses from at least some of the storageunits within a response timeframe; when the received read sliceresponses include less than a decode threshold number of encoded dataslices of a set of encoded data slices, generate at least one forcedread slice request for an encoded data slice other than the receivedencoded data slices; send the at least one forced read slice requests toat least one other storage unit of the storage set; and when receivingthe decode threshold number of encoded data slices, dispersed storageerror decode the received decode threshold number of encoded data slicesto reproduce a data segment of the recovered data.
 12. The computingdevice of claim 11, wherein the issuing includes: generating the readslice requests, selecting the storage units and sending the read slicerequests to the selected storage units.
 13. The computing device ofclaim 12, wherein the selecting the storage units is based on one ormore of: a predetermination, a storage unit performance level, a storageunit availability level, or a random selection.
 14. The computing deviceof claim 12, wherein the sending includes sending to a storage unitoutside of the selected storage units.
 15. The computing device of claim11, wherein the generating is based on determining a number of forcedread slice requests based on a number of received encoded data slices.16. The computing device of claim 15, wherein the generating furtherincludes determining a number of forced read slice request to generatebased on a difference between the decode threshold number and a numberof received encoded data slices.
 17. The computing device of claim 11,wherein the sending includes sending to a storage unit that correspondsto an error response indicating no availability unless powered up. 18.The computing device of claim 11, wherein the sending includes sendingto temporary storage locations.
 19. The computing device of claim 18,wherein the temporary storage locations include any of: SSDs, RAM, orother memory devices.
 20. The computing device of claim 19, wherein,when the temporary storage locations become full or near full, or whenthe memory device for which the encoded data slices are destined comesout of power-save-mode (PSM), then the storage unit flushes thesetemporary locations by moving the encoded data slices to the memorydevice for which it was originally destined.